This invention relates to a joint assembly for use in a robot mechanism.
In general, it is preferable that a robot mechanism is movable like a human arm which can be moved in various manners. Specifically, the human arm can move a human hand around an elbow along a spherical surface and can be swiveled with respect to the elbow, with an arm axis drawing a cone-shaped surface. As regards swiveling the human arm, it is to be noted that the human arm itself may never be rotated about the arm axis. In other words, the human arm can be swiveled with respect to the elbow with a rotation or twist of the human arm itself suppressed about the arm axis.
In order to simulate such a motion of the human arm, the robot mechanism should comprise an intricate and heavy joint assembly, as will later be described with reference to a few figures of the accompanying drawing. In addition, such an intricate joint assembly results in difficulty of control.
In a paper contributed by Shigeo Hirose et al to the Institute of Measurement and Automatic Control Engineers of Japan, Vol. 17, pages 686-692 (No. 6, September 1981), a so-called oblique swivel joint is proposed to form a joint model and comprises a first link member which has a first link axis, a first slant end oblique to the first link axis, a second link member which has a second link axis concurrent with the first link axis, and a second slant end guided along the first slant end. The second slant end is rotated along the first slant end about the second link axis by a motor fixed to the first slant end.
As will later be described with reference to the other figures of the accompanying drawing, the second link member can be swiveled along a cone-shaped surface drawn by the second link axis. However, it is to be noted that the second link member itself is inevitably automatically rotated about the second link axis by the motor. Therefore, the proposed joint assembly can never simulate the motion of the human arm.